Table 1. Baseline characteristics of patients starting long-term oxygen therapy for chronic obstrucitve pulmonary disease, 1992–2008.

Characteristic	Women, n = 4,783 (55%)	Men, n = 3,929	P-value
Age, years	71.8±8.4	73.7±7.8	<0.001
PaO2 air, kPa	6.5±0.9	6.7±0.9	<0.001
PaCO2 air, kPa	6.5±1.2	6.1±1.2	<0.001
PaO2 oxygen, kPa	8.8±1.1	8.9±1.1	<0.001
PaCO2 oxygen, kPa	6.8±1.2	6.3±1.2	<0.001
FEV1, L	0.7±0.3	1.0±0.5	<0.001
FEV1 of predicted, %	34.0±17.0	35.5±19.6	0.005
FVC, L	1.5±0.5	2.2±0.9	<0.001
Smoking history, %
Never	6	4	<0.001
Past	91	94	<0.001
Current	3	2	0.129
All Hospitalizations, n*	5 (3–9)	5 (3–9)	0.013
Hospitalizations for COPD, n*	2 (1–4)	2 (1–4)	<0.001
In-hospital days*	48 (25–87)	41 (21–77)	<0.001

Data presented as mean ± SD unless otherwise specified.

Definition of abbreviations: FEV₁ = forced expiratory volume in one second; FVC = forced vital capacity; Pa_CO2 air = arterial blood gas tension of carbon dioxide while breathing ambient air; Pa_CO2 oxygen = arterial blood gas tension of carbon dioxide while breathing oxygen; Pa_O2 air = arterial blood gas tension of oxygen while breathing ambient air; Pa_O2 oxygen = arterial blood gas tension of oxygen while breathing oxygen.

^*Hospitalizations and in-hospital days within 5 years prior to starting LTOT, presented as median (first quartile – third quartile).